The present invention relates to a tensioning device which is used to select and impart a moment of torque to a shaft. The present tensioning device has been found to be particularly useful in connection with conveyor belt cleaners which utilize scraper blades to clean a conveyor belt. Conveyor belt scraper blades are conventionally mounted on a shaft which is positioned transverse to the direction of conveyor belt travel. When the shaft is rotated, the blades are forced into contact with the belt to scrape off adherent material. Over time the scraper blades wear and lose contact with the belt thereby hampering the blades cleaning ability. The shaft on which the scraper blades are mounted must then be rotated to reposition the scraper blades against the belt with the desired amount of force.
Conveyor belt scraper blades are subjected to repeated impact forces which are generated by the blades coming into contact with conveyor belt splices, with enlarged pieces of the conveyed material, or other debris which adheres to the belt, all of which can cause appreciable damage to the scraper blades or the conveyor belt cleaning mechanism. To promote effective cleaning of the conveyor belt and to avoid shutting the belt down for repair, it is of the utmost importance to provide the scraper blades with a shock absorbing capability.
Previous torsional tensioning devices of the types shown in U.S. Pat. No. 4,533,036 and 4,925,434 and in U.S. patent application Ser. No. 561,969, filed Aug. 2, 1990 entitled "Spring Steel Tensioner" have been used in connection with conveyor belt scraper blades. In these devices the biasing means extends in a generally linear direction which is substantially parallel and concentric to the central axis of the conveyor belt cleaner shaft. In each of these devices the biasing means is torsionally rotated such that one end of the biasing means is rotated about the longitudinal axis of the biasing means with respect to the other end of the biasing means. In other words, the biasing means is twisted about its central longitudinal axis. A torsional force is thereby created and stored within the biasing means which provides the torsional biasing force to rotate the cleaner shaft. In each of these devices the torsional force which is applied to the tensioner by the user equals the torsional force generated in the biasing means and in the shaft. The torsional force in the biasing means can not be varied without affecting the torsional force applied to the shaft. Torsional springs used for mounting a conveyor belt cleaner to a shaft are shown in U.S. Pat. Nos. 3,674,131 and 4,533,035. A torsion spring is also shown in U.S. Pat. No. 4,171,920.